efi/x86: Move x86 back to libstub

This reverts commit 84be880560fb, which itself reverted my original
attempt to move x86 from #include'ing .c files from across the tree
to using the EFI stub built as a static library.

The issue that affected the original approach was that splitting
the implementation into several .o files resulted in the variable
'efi_early' becoming a global with external linkage, which under
-fPIC implies that references to it must go through the GOT. However,
dealing with this additional GOT entry turned out to be troublesome
on some EFI implementations. (GCC's visibility=hidden attribute is
supposed to lift this requirement, but it turned out not to work on
the 32-bit build.)

Instead, use a pure getter function to get a reference to efi_early.
This approach results in no additional GOT entries being generated,
so there is no need for any changes in the early GOT handling.

Tested-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/drivers/firmware/efi/Makefile b/drivers/firmware/efi/Makefile
index aef6a95..d8be608 100644
--- a/drivers/firmware/efi/Makefile
+++ b/drivers/firmware/efi/Makefile
@@ -7,4 +7,4 @@ obj-$(CONFIG_EFI_VARS_PSTORE)		+= efi-pstore.o
 obj-$(CONFIG_UEFI_CPER)			+= cper.o
 obj-$(CONFIG_EFI_RUNTIME_MAP)		+= runtime-map.o
 obj-$(CONFIG_EFI_RUNTIME_WRAPPERS)	+= runtime-wrappers.o
-obj-$(CONFIG_EFI_ARM_STUB)		+= libstub/
+obj-$(CONFIG_EFI_STUB)			+= libstub/